Teams reach for positional need, especially if that position is RD.
This feels like where most draft mistakes get made. Teams rationalize picking for position when the BPA is a player that plays a position they don't need.
The biggest mistake here is assuming you know what your team is going to need or look like 3+ years down the road.
A bad example of this is the Devils picking Nemec 2nd overall in 2022 (though I think you can justify that he really may have been seen as the BPA). The Devils passed over the (IMO) superior prospect in Cooley because it felt like RD was a future need, not knowing we'd draft Casey in the next round and then sign Pesce. Now we have a logjam at RD but could really use a kid like Cooley to center our 3rd line. That's not to say Nemec isn't amazing, but if Devils management knew what the team looked like now, it makes me wonder if they would take Nemec again.
The history of taking defenseman in the top 5 of the draft is pretty ugly in the last 20 years (excluding last few years for because these kids are still developing). Of the 20 dmen drafted in the top 5 from 2004 to 2017, I count only 6-7 true #1 dmen, with 3 complete busts, 7 bottom to mid pair dmen, and 3 #2Ds. The recent history does look a bit more promising, but there's a lot up in the air.
The history is especially bad though when you look at team's drafting big (6'3+) dmen in the top 10. From 2004 - 2017, there were 24 dmen picked in the top 10 that were 6'3+:
13 of which I would consider busts or major disappointments
Griffin Reinhart
Boris Valabik
Dylan McIlrath
Brian Lee
Keaton Ellerby
Cam Barker
Jared Cowen
Ladislav Smid
Haydn Fleury
Karl Alzner
Zach Bogosian
Erik Gudbranson
Rasmus Ristolainen
And 12 who were good enough to be a top pair Dman for 5+ years
Erik Johnson
Darnell Nurse
Dougie Hamilton
Adam Larsson
Hampus Lindholm
Jacob Trouba
Noah Hanifin
Aaron Ekblad
Seth Jones
Mikhail Sergachev
Alex Pietrangelo
Victor Hedman
Even the group of successful players is pretty thin, with a lot of guys who had very short lived primes and who became liabilities by the time they were 30. I would say there's only 3-4 guys on this list who had 10+ year primes where they were top pairing defenseman. Hedman is the only Norris winner of the group.